Image processing apparatus

ABSTRACT

There is disclosed an image processing apparatus in which a pattern table stores a plurality of screen patterns which include a predetermined number of pattern data and have different data patterns. An in-pattern position calculator generates an in-pattern position signal indicating a position of an input image signal in the screen pattern from main and sub scanning synchronizing signals. A pattern selecting signal combining section generates a pattern selecting signal for selecting a specified pattern in the pattern table from the input image signal, combines the pattern selecting signal and the in-pattern position signal supplied from the in-pattern position calculator, and supplies an address in the pattern table. A controller reads pattern data corresponding to the address in the pattern table from the pattern table and supplies image data.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a half tone processing for usein image forming apparatuses such as a digital copying apparatus,particularly to an image processing apparatus for reproducing a halftone image by a screen processing.

[0002] An object of a screen processing is consider properties ofrecording apparatuses arranged in subsequent stages, modulate an inputimage signal to a mesh-dot image or multi-line form, and reproduce ahalf tone image. In the mesh-dot image form, a plurality of outputteddots form one mass, and the masses are regularly arranged like meshes ofa net in the image.

[0003] In the screen processing of a multi-line system, a width of anoutput pixel is changed in accordance with a value of the input imagesignal and half tone is represented. There has heretofore been atechnique of comparing a triangular wave or another reference signaloutputted from an analog circuit with the input image signal and forminga multi-line screen. That is, a comparator compares a monotonouslyincreasing or decreasing triangular wave with an image signal obtainedby D/A conversion of input image data in a period of one or severalpixels. For example, when an amplitude of the triangular wave is largerthan that of the image signal, “H” is outputted (i.e., laser is turnedON), and the image is formed in the pixel. A period of the triangularwave is the same as that of the image signal. When the monotonouslyincreasing triangular wave is used, the image is formed, for example, ona right side in the pixel. When the monotonously decreasing triangularwave is used, the image is formed, for example, on a left side in thepixel.

[0004] A type of an outputted image pattern is limited in theaforementioned conventional screen processing. That is, since aconstitution is fixed, various screen patterns cannot be handled.

SUMMARY OF THE INVENTION

[0005] An object of the present invention is to realize various screenprocessings such as a multi-line with a simple system constitution.

[0006] In order to achieve the above object, according to one aspect ofthe present invention, there is provided an image processing apparatuscomprising: a pattern table which stores a plurality of screen patternsincluding a predetermined number of pattern data and having differentdata patterns; an in-pattern position calculator which generates anin-pattern position signal indicating a position of an input imagesignal in the screen pattern from a main scanning synchronizing signaland a sub scanning synchronizing signal; a pattern selecting signalcombining section which generates a pattern selecting signal whichselects a specified pattern in the pattern table from the input imagesignal, combines the pattern selecting signal with the in-patternposition signal supplied from the in-pattern position calculator, andsupplies an address in the pattern table; and a pattern table readingsection which reads pattern data corresponding to the address in thepattern table from the pattern table and supplying image data.

[0007] Various screen processings such as a mesh-dot image and amulti-line are easily realized by rewriting data in the pattern table.In this manner, different from a method of using a systematic ditherprocessing to form a screen, in the present invention there is not acomparator which compares the input image signal with the pattern data.

[0008] The pattern table has an index for associating the inputted imagesignal with the screen pattern data, and an association between theimage signal and the screen pattern data is changed by rewriting theindex in the pattern table.

[0009] According to another aspect of the present invention, there isprovided an image processing apparatus comprising: a pattern table whichstores a plurality of screen patterns including a predetermined numberof pattern data and having different data patterns; an in-patternposition calculator which generates an in-pattern position signalindicating a position of an input image signal in the screen patternfrom a main scanning synchronizing signal and a sub scanningsynchronizing signal; a pattern selecting signal combining section whichgenerates a pattern selecting signal for selecting a specified patternin the pattern table from the input image signal, and calculates anaddress in the pattern table and data for interpolation for use in aninterpolation processing from the pattern selecting signal and thein-pattern position signal supplied from the in-pattern positioncalculator; an interpolation original data reading section which readstwo consecutive pattern data in an address space of the pattern table asinterpolation original data from the pattern table based on the addressin the pattern table calculated by the pattern selecting signalcombining section; and an interpolation processor which uses the datafor interpolation calculated by the pattern selecting signal combiningsection, subjects the two interpolation original data read by theinterpolation original data reading section to the interpolationprocessing, and supplies a result of the interpolation processing asimage data.

[0010] An enormous storage capacity is necessary for storing screenpattern information in accordance with all signal levels of the inputimage signal. However, in the present invention, only the screen patterninformation corresponding to a specified signal in a signal range isstored as described above, and interpolated and used as the occasiondemands. Therefore, the storage capacity for use can remarkably bereduced.

[0011] Moreover, in a recording apparatus for using a pulse width signaland pulse position signal to record the image, the screen patterninformation regarding the pulse width signal and pulse position signalis separated, and a plurality of screen pattern information regarding acertain pulse position signal are set to be the same in accordance withthe image signal level. Therefore, the storage capacity for use can bereduced.

[0012] Furthermore, a block averaging processor which divides the inputimage into small blocks, and averaging the image data in each block isdisposed in a previous stage of the aforementioned screen processing.Therefore, a more possibly generated by periodic property of the inputimage signal can be removed.

[0013] Additionally, when the reading address of the screen patterntable is changed for each signal channel (cyan, magenta, yellow, black,and the like), different screens can be formed with one pattern table(for one channel).

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a sectional view showing an internal structure of adigital copying apparatus 10 to which the present invention is applied.

[0015]FIG. 2 is a block diagram schematically showing a constitution ofa control system of the digital copying apparatus to which the presentinvention is applied.

[0016]FIG. 3 is a block diagram showing a schematic constitution of apattern selecting processor for performing a direct pattern selectingmethod.

[0017]FIG. 4 shows an in-pattern position Loc in a screen pattern havinga size of 4×4.

[0018]FIGS. 5A to 5C show pattern data examples of the 4×4 screenpattern.

[0019]FIG. 6 shows a change of the in-pattern position Loc in a patternimage.

[0020]FIG. 7 shows a relation of an address Adr of a pattern table withthe pattern data.

[0021]FIG. 8 shows a constitution of the pattern selecting processoraccording to a second embodiment of the present invention.

[0022]FIGS. 9A to 9E are explanatory views of a reference position.

[0023]FIG. 10 shows a constitution of the pattern selecting processoraccording to a third embodiment of the present invention.

[0024]FIG. 11 is a block diagram showing a constitution of an imageprocessor according to a fourth embodiment of the present invention.

[0025]FIG. 12 shows a schematic constitution of a block averagingsection of FIG. 11.

[0026]FIG. 13 is an explanatory view of a block averaging processing.

[0027]FIG. 14 shows a constitution example of a block averagingprocessing parameter.

[0028]FIG. 15 is a block diagram showing a constitution of the imageprocessor according to a fifth embodiment of the present invention.

[0029]FIG. 16 shows a constitution of the pattern selecting processoraccording to a sixth embodiment of the present invention.

[0030]FIG. 17 shows a constitution of the pattern selecting processoraccording to a seventh embodiment of the present invention.

[0031]FIG. 18 shows a constitution of the pattern selecting processoraccording to an eighth embodiment of the present invention.

[0032]FIG. 19 shows a constitution of the pattern selecting processoraccording to a ninth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Preferred embodiments of the present invention will be describedhereinafter with reference to the drawings.

[0034]FIG. 1 is a sectional view showing an internal structure of adigital copying apparatus 10 to which the present invention is applied.The digital copying apparatus 10 includes a scanner 4 which functions asreading means, and a printer 6 which functions as image forming means asdescribed later.

[0035] An original base 12 formed of transparent glass on which areading object, that is, a draft D is laid is disposed on an uppersurface of the digital copying apparatus 10. Moreover, an automaticdraft feeder 7 (hereinafter referred to as ADF) for automaticallyfeeding the draft D onto the draft base 12 is disposed on the uppersurface of the digital copying apparatus 10. The ADF 7 is disposed to beopenable/closable with respect to the draft base 12, and also functionsas a draft press for attaching the draft D laid on the draft base 12 tothe draft base 12.

[0036] The scanner 4 disposed in the digital copying apparatus 10 has anexposure lamp 25 as a light source for irradiating the draft D laid onthe draft base 12, and a first mirror 26 for deflecting a reflectedlight from the draft D in a predetermined direction. These exposure lamp25 and first mirror 26 are attached to a first carriage 27 disposedunder the draft base 12.

[0037] The first carriage 27 is disposed to be movable in parallel tothe draft base 12, and is reciprocated/moved under the draft base 12 bya driving motor 38 via a toothed belt (not shown).

[0038] Moreover, a second carriage 28 movable in parallel to the draftbase 12 is disposed under the draft base 12. Second and third mirrors30, 31 for successively deflecting the reflected light deflected fromthe draft D by the first mirror 26 are attached to the second carriage28 and disposed at right angles to each other. The second carriage 28 isdriven with respect to the first carriage 27 via the toothed belt, andthe like for driving the first carriage 27, and moved along the draftbase 12 and in parallel to the first carriage 27 at a ½ speed.

[0039] Furthermore, an image forming lens 32 for focusing the reflectedlight from the third mirror 31 on the second carriage 28, and a CCDsensor 34 for receiving and photoelectrically converting the reflectedlight focused by the image forming lens 32 are disposed under the draftbase 12.

[0040] On the other hand, the printer 6 includes a laser exposure device40 which functions as an exposure scanning device. The laser exposuredevice 40 includes a semiconductor laser 41 as a light source, a polygonmirror 36 as a scanning member for continuously deflecting a laser lightemitted from the semiconductor laser 41, a polygon motor 37 as ascanning motor for rotating/driving the polygon mirror 36 at apredetermined number of rotations, and a laser optical system 42 fordeflecting the laser light from the polygon mirror 36 and guiding thelaser light to a photosensitive drum 44 as described later.

[0041] The semiconductor laser 41 is controlled to turn on/off inaccordance with image information, and the like of the draft D read bythe scanner 4. In the laser exposure device 40, the laser light isdirected to the photosensitive drum 44 via the polygon mirror 36 andlaser optical system 42, and scanned on a peripheral surface of thephotosensitive drum 44 to form an electrostatic latent image on theperipheral surface of the photosensitive drum 44. Disposed in aperiphery of the photosensitive drum 44 are: an electric charger 45 forcharging the peripheral surface of the photosensitive drum 44 at apredetermined potential before the image is formed on the peripheralsurface; a developing unit 46 as developing means for supplying toner asa developer to the electrostatic latent image formed on the peripheralsurface of the photosensitive drum 44 and developing the image at adesired image density; a stripping charger 47 for separating an imageforming material supplied from a paper cassette described later, thatis, a copy paper P from the photosensitive drum 44; a transfer charger48 for transferring a toner image formed on the photosensitive drum 44to the paper P; a stripping pawl 49 for stripping the copy paper P fromthe peripheral surface of the photosensitive drum 44; a cleaner 50 forcleaning toner remaining on the peripheral surface of the photosensitivedrum 44; and a static eliminator 51 for eliminating electricity of theperipheral surface of the photosensitive drum 44 in order. Thephotosensitive drum 44, a developing roller (not shown) in thedeveloping unit 46, and the like are rotated/driven by a main motor 77.

[0042] An upper cassette 52, middle cassette 53, and lower cassette 54which can be drawn from an apparatus main body, respectively, arestacked and disposed in a lower part of the digital copying apparatus10, and a large-capacity feeder 55 is disposed on the side of theapparatus. The copy paper P having different sizes or directions isloaded in the respective cassettes.

[0043] In the digital copying apparatus 10, a conveying path 58 isextended through a transfer section positioned between thephotosensitive drum 44 and the transfer charger 48 from the respectivecassettes and large-capacity feeder 55. A fixing device 60 having afixing lamp 60 a and a heat roller 60 b to which heat is given by thefixing lamp 60 is disposed in a terminal end of the conveying path 58. Adischarge port 61 is formed in a side wall of the digital copyingapparatus 10 and disposed opposite to the fixing device 60, and afinisher 150 including a single tray is attached to the discharge port61.

[0044]FIG. 2 is a block diagram schematically showing a constitution ofa control system of the digital copying apparatus to which the presentinvention is applied.

[0045] The digital copying apparatus is constituted of a main controller90 controlled by a system CPU 91, the scanner 4 controlled by a scannerCPU 100, the printer 6 controlled by a printer CPU 110, and a controlpanel 80 controlled by a panel CPU 83.

[0046] The main controller 90 is constituted of the system CPU 91, a ROM92, a RAM 93, a NVRAM 94, a shared RAM 95, an image processor 96, a pagememory controller 97, a page memory 98, a printer font ROM 121, ahorizontal synchronizing signal generation circuit 123, an imagetransfer clock generation circuit 124, and a facsimile interface 130.

[0047] The ROM 92 stores various control programs including the presentinvention. The system CPU 91 uses the RAM 93 as a work area, andcontrols the whole main controller 90 in accordance with the controlprogram stored in the ROM 92. The system CPU 91 transmits an operationinstruction to the printer 6 (printer CPU 110) and scanner 4 (scannerCPU 100), and the printer 2 and scanner 4 return a status to the systemCPU 91.

[0048] The nonvolatile RAM (NVRAM) 94 is a nonvolatile memory backed upby a battery (not shown). When power is turned off, data on the NVRAM 94is held. Moreover, the NVRAM 94 stores a default value (initial setvalue) for hardware elements constituting a photographic copying (PPC)function, FAX function, and the like. The shared RAM 95 is used toperform bi-directional communication between the system CPU 91 and theprinter CPU 110.

[0049] The image processor 96 performs an image processing of thepresent invention, such as a screen processing, trimming, and maskingwith respect to the image data inputted from the scanner 4, and thelike. The printer font ROM 121 stores font data corresponding to codedata of a character or another code.

[0050] A printer controller 99 receives the code data of the characteror another code from external apparatuses such as a personal computervia LAN. The printer controller 99 uses font data stored in the printerfont ROM 121 to develop the code data into image data and store theimage data in the page memory 98 with a character size attached to thecode data, and a size and resolution corresponding to the dataindicating the resolution.

[0051] The horizontal synchronizing signal generation circuit 123generates a horizontal synchronizing signal in synchronization withrotation of the polygon mirror 36. The image transfer clock generationcircuit 124 generates an image transfer clock to control a timing fortransferring the image data.

[0052] The page memory controller 97 stores or read the image data withrespect to the page memory 98. The page memory 98 has an area in whichthe image data, for example, for two pages can be stored, and has aconstitution in which data obtained by compressing the image data fromthe scanner 4 or the printer controller 99 can be stored by a unit ofone page.

[0053] The printer 6 is constituted of: the printer CPU 110 forcontrolling the whole printer 6; a ROM 111 in which control program, andthe like are stored; a RAM 112 for storing data; an LD drive circuit 113for controlling light emission by the semiconductor laser 41 to turnon/off; a polygon motor drive circuit 114 for controlling the polygonmotor 37 of the laser unit 40; a paper conveyor 115; a developingprocessor 116; a fixing controller 117; an optional section 118, and amain motor drive circuit 119.

[0054] The scanner 4 includes the scanner CPU 100, a ROM 101, a RAM 102,a CCD driver 103, a scanner motor driver 104, and an image corrector105. The scanner CPU 100 controls the whole scanner 4, the ROM 101stores the control program, and the like, and the RAM 102 is used fortemporarily storing the data. The CCD driver 103 drives the CCD sensor34, and the scanner motor driver 104 controls rotation of the drivingmotor 38 for moving the first and second carriages 27, 28 of theexposure lamp 25 and mirrors 26, 30, 31. The image corrector 105includes: an A/D conversion circuit for converting an analog signal fromthe CCD sensor 34 to a digital signal; and a shading correction circuitfor correcting a fluctuation of a threshold level with respect to anoutput signal from the CCD sensor 34, which is caused by a dispersion ofthe CCD sensor 34, an ambient temperature change, and the like.

[0055] A first embodiment of the screen processing according to thepresent invention now will be described. The embodiment is called adirect pattern selecting method. FIG. 3 is a block diagram showing aschematic constitution of a pattern selecting processor 96 a forperforming the direct pattern selecting method. This pattern selectingprocessor 96 a is a processor included in the image processor 96,constituted of an in-pattern position calculator 201, pattern selectingsignal combiner 202, and a pattern table 203, and generally controlledby the system CPU 91.

[0056] The pattern selecting method is a screen processing methodcomprising: reading data corresponding to a position in the pattern ofthe image signal from a screen pattern corresponding to a value of aninputted image signal Pin; and outputting the data. The image signal Pinis, for example, eight-bit data, and a plurality of screen patterns arestored in the pattern table 203.

[0057] First, calculation of an in-pattern position will be describedhereinafter. An in-pattern position Loc represents an internalcoordinate of two-dimensional screen pattern in one dimension. FIG. 4shows an example of the in-pattern position Loc in the screen patternhaving a size of 4×4. In FIG. 4, xd1, yd1 denote pattern sizes. As shownin FIG. 4, the in-pattern position Loc is indicated by a left uppervalue 00H to a right lower value 0FH (H denotes hexadecimal).

[0058] Moreover, FIGS. 5A to 5C show examples of the 4×4 screen pattern(pattern data). FIG. 5A shows the pattern selected when the input imagesignal Pin is of 10H, FIG. 5B shows the pattern selected when the signalis of 20H, and FIG. 5C shows the pattern selected when the signal is of40H. In this manner, the screen patterns of different data patterns arestored in accordance with a value (density) of the image signal.

[0059]FIG. 6 shows a change of the signal Loc in a real image or aprocessing object image (a content of an averaging processing describedlater is also shown). This shows a pattern image with xd1=yd1=4, xds1=0.Here, xds1 is an offset amount by which the pattern is shifted in a mainscanning direction for each sub scanning period of the pattern (this canmake an angle in arrangement of the patterns).

[0060] The in-pattern position Loc (eight or more bits) is calculatedfrom an X coordinate value x (main scanning direction) and Y coordinatevalue y (sub main scanning direction)of a noted image, which areobtained by counting main and sub scanning synchronizing signals asfollows.

[0061] yy=y%yd1

[0062] yya=(y/yd1)%xd1

[0063] xx=(x+yya*xds1)%xd1

[0064] Loc=yy*xd1+xx

[0065] * a/b denotes an integer portion of a quotient of a time at whicha is divided by b.

[0066] * a%b denotes a surplus of the time at which a is divided by b.

[0067] The pattern selecting signal combiner 202 now will be described.The pattern selecting signal combiner 202 combines lower eight bits ofthe in-pattern position Loc with eight bits of the input image signalPin (all bits of both in the present embodiment) as follows. The eightbits of the input image signal Pin constitute a pattern selectingsignal. The pattern selecting signal combiner 202 outputs a combinedresult as an address signal Adr.

[0068] Adr=Combination of lower 8 bits of Loc and upper 8 bits of Pin.

[0069] *Combine the bits so that Loc indicates the upper bits and Pinindicates the lower bits.

[0070] The pattern table 203 and table reference output Pout now will bedescribed. As shown in FIG. 7, a plurality of pattern data are stored inaccordance with Adr in the pattern table 203. A numeric value inparentheses is an address Adr. As shown in FIG. 7, for the address Adr,0000H to 00FFH are allotted from upper to lower end of a left-endcolumn, 0100H to 01FFH are allotted from the upper to lower end of thenext column, and 0F00H to 0FFFH are allotted from the upper to lower endof a right-end column. Each row corresponds to each screen pattern. FIG.7 is a pattern table with a pattern size of 4×4, and input image signalof eight bits. When the pattern size or the image signal is larger thanthis value, the pattern table is enlarged rightwards or downward in FIG.7.

[0071] The pattern data corresponding to the address Adr in the patterntable, in which the input image signal Pin and position signal Loc arecombined, is read under control of the controller, and supplied as thetable reference output Pout (half tone processing output). Here,“ditw1[i]” means an i-th element of the pattern table. That is, Pout isrepresented as follows.

[0072] Pout=ditw1[Adr]

[0073] Additionally, for example, a table including 65536 elements isrepresented by “ditw1 (65536)”. The table reference output Pout issupplied as eight-bit data or pulse width signal.

[0074] When the in-pattern position Loc is the same, the pattern datastored in the pattern table 203 may be set to monotonously change(increase or decrease) in accordance with a size of the patternselecting signal (eight bits of the image signal Pin). Alternatively,the data may be set in such a manner that an increase/decrease directionchanges in at least one portion. According to the present embodiment,various screen processing such as a mesh-dot image or a multi-line caneasily be realized by rewriting the data in the pattern table 203.

[0075]FIG. 8 shows a constitution of a pattern selecting processor 96 baccording to a second embodiment of the present invention. The patternselecting processor 96 b supplies the pulse width signal as the outputPout. Different from the pattern selecting processor 96 a of FIG. 3, areference position table 204 for outputting a pulse position signal, anda signal combiner 206 are added.

[0076] A pulse reference position indicates that the image is formedfrom a left end, from a right end, or in a center portion in a pixel.FIGS. 9A shows a 3×2 reference position table as one example of thereference position table. In the reference position table, “03”indicates that the image is formed from the right end in the pixel, “02”indicates that the image is formed from the left end, and “00” indicatesthat the image is formed in the center portion. Therefore, in thereference position table of FIG. 9A, as shown by arrows of FIG. 9B, theimage is formed in accordance with a pixel value. The reference positiontable is repeatedly applied, and values of the reference position tableare obtained in one scanning line as shown in FIG. 9C.

[0077] When the value of the pulse width signal is obtained in theposition corresponding to each element of the 3×2 reference positiontable, for example, as shown in FIG. 9D, an output image OP1 is obtainedas shown in FIG. 9E. FIG. 9E shows output images OP1 and OP2, and showsthat the reference position table of FIG. 9A is shifted and applied foreach sub scanning of the reference position table.

[0078] In the present embodiment shown in FIG. 8, similarly as thepattern shown in FIG. 4, the reference position table 204 has a size of4×4. Therefore, based on the in-pattern position Loc calculated by thein-pattern position calculator 201, the reference position table (dits1)204 is referred to under the control of the system CPU 91, the referenceposition data corresponding to Loc is read, and a pulse position signalPS1 is supplied. That is, the pulse position signal PS1 is representedas follows.

[0079] PS1=dits1[Loc]

[0080] The signal combiner 206 combines a pulse width signal Pout1supplied from the pattern table 203 and the pulse position signal PS1supplied from the reference position table 204, and generates an imagesignal Pout2 having a width corresponding to the pulse width signalPout1 in the reference position in each output pixel.

[0081]FIG. 10 shows a constitution of a pattern selecting processor 96 caccording to a third embodiment of the present invention. The patternselecting processor 96 c is constituted by adding an interpolationprocessor 205 to the pattern selecting processor 96 b. The interpolationprocessor 205 performs an interpolation processing based on two pulsewidth signals P1 and P2 read from a pattern table 207.

[0082] The pattern selecting signal combiner 202 combines lower eightbits of the in-pattern position Loc outputted from the in-patternposition calculator 201 and upper eight bits of the input image signalPin (e.g., ten bits). A combined result is outputted as the addresssignal Adr (16 bits).

[0083] Adr=combination of lower 8 bits of Loc and upper 8 bits of Pin

[0084] The pattern selecting signal combiner 202 further separates 16bits of address signal Adr into upper 13 bits and lower three bits, andoutputs ADH, ADL as follows.

[0085] ADH=upper 13 bits of Adr

[0086] ADL=lower 3 bits of Adr

[0087] Under the control of the system CPU 91, the pattern table 207(ditw1 (8192)) is referred to based on an address upper ADH, and ADH isconverted to interpolation original signals P1 and P2 as follows.

[0088] P1=ditw1[ADH]

[0089] P2=ditw1[ADH+1]

[0090] Here, P1 is pattern data stored in address ADH of the patterntable 207, and P2 is pattern data stored in address (ADH+1). That is,the CPU 91 reads two pattern data consecutive in an address space in thepattern table 207.

[0091] Additionally, ADH=8191, then ADH+1=8192, and 8192 is out of arange of pattern table ditw1[8192]. This is because the address of thepattern table ditw1[8192] is in a range of 0 to 8191. However, in thiscase, ditw1[ADH+1], that is, P2 is not referred to in the subsequentstage, and therefore a value of P2 may be indefinite.

[0092] The interpolation processor 205 uses the interpolation originalsignals P1 and P2 to perform the following interpolation processing, andoutputs the output value Pout (or Pout 2) as the pulse width signal.

[0093] ADW=lower 7 bits of ADH;

[0094] if (ADW<127), Pout=(P2*ADL+P1*(8−ADL)/8;

[0095] if (ADW=127), Pout=P1.

[0096] For example, when ADW is smaller than 127, P1 is 100, P2 is 110,and ADL is 5, Pout is as follows. $\begin{matrix}{{Pout} = \quad {\left( {{110*5} + {100*\left( {8 - 5} \right)}} \right)/8}} \\{= \quad 106.25} \\{\quad \text{omitting~~decimals,}} \\{= \quad 106}\end{matrix}$

[0097] That is, the interpolation processor 205 subjects the patterndata P1 and P2 to a linear interpolation processing using ADL.

[0098] The pattern selecting processor 96 b of FIG. 8 directly refers tothe pattern table and determines the pulse width signal. However, thepattern selecting processor 96 c of the present embodiment decreases thenumber of screen patterns in order to reduce a storage capacity of thepattern table, and obtains omitted pattern data in the interpolationprocessing.

[0099] Also in the pattern selecting processor 96 c, under the controlof the system CPU 91, the pulse reference position table (dits1) 204 isreferred to based on the in-pattern position Loc, and the pulse positionsignal PS1 is provided as follows.

[0100] PS1=dits1[Loc]

[0101]FIG. 11 is a block diagram showing a constitution of the imageprocessor according to a fourth embodiment of the present invention. Inthe fourth embodiment, a block averaging section 96 d, and γ correctionprocessor 96 e are added in this order to the previous stage of thepattern selecting processor.

[0102] In FIG. 11, the block averaging section 96 d divides the inputimage into areas (blocks) based on the main and sub scanningsynchronizing signals, and converts the signals in order to average thedivided areas.

[0103]FIG. 12 shows a schematic constitution of the block averagingsection 96 d. The block averaging section 96 d is constituted of aninput line buffer (line memory) 208, a work memory 209 formed of aplurality of line memories, an output line buffer (line memory 210, anarea divider 211, and an averaging unit 212.

[0104] The image signal Pin inputted to the input line buffer 208 isshifted in an arrow direction and stored as the image data in the inputline buffer 208. The image data for one line stored in the input linebuffer 208 is copied to a last line memory 209L of the work memory 209by a line unit in response to the sub scanning synchronizing signal. Inthe work memory 209, the image data is copied into the next line memoryby the line unit in a fast in fast out (FIFO) form in response to thesub scanning synchronizing signal. The data in a front line memory 209Fof the work memories is copied to the output line buffer 210 before acopy operation from the previous line memory. The image data copied intothe output line buffer 210 is shifted in the arrow direction in responseto the main scanning synchronizing signal, and outputted to thesubsequent γ correction processor 96 e.

[0105] The area divider 211 counts the main and sub scanningsynchronizing signals, and outputs an area coordinate of a rectangularblock in the work memory 209 to the averaging unit 212 at a time whenpredetermined area division, for example, rectangular block division ispossible. The averaging unit 212 having received the area coordinateperforms a processing of averaging the values in the block of thedesignated area in the work memory 209, and burying the value in theblock.

[0106] The area division by a periodic rectangular block will bedescribed as an example. The averaging unit 212 averages the input imagesignals Pin in a predetermined rectangular block, and stores an averagevalue as the image signal of each pixel of the block again in the workmemory 209.

[0107]FIG. 13 shows a schematic diagram of a block averaging processing.It is assumed that an averaging block is rectangular and has a size ofxa1 pixels in a main scanning direction and ya1 pixels in a sub scanningdirection (1≦xa1≦6, 1≦ya1≦3). A start point of the averaging block inthe image is (xai1, yai1), and the averaging blocks are shifted by thexas1 pixels in a negative main scanning direction (or xa1−xas1 in apositive direction) for every yas1 blocks in the sub scanning direction.In FIG. 13, xai1=1, yai=1, xa1=3, ya1=2, xas1=2(=−1), yas1=3.

[0108] In averaging calculation, a sum of pixel values, in a rectangleis obtained and divided by the number of pixels in the block. Fordecimals, numbers of one are rounded up and anything under one isrounded down (binary). A block which is bx-th in the main scanningdirection, and by-th in the sub scanning direction is B[bx, by]. Then, apixel range of the block B[bx, by] is a rectangle which has thefollowing four points as four corners.

[0109] α1:(xbs, ybs), α2:(xbs+xa1−1, ybs),

[0110] α3:(xbs, ybs+ya1−1), α4:(xbs+xa1−1, ybs+ya1−1)

[0111] Additionally, xbs, ybs are as follows.

[0112] xbs=xai1+xa1·bx−Int(by/yas1)*xas1

[0113] ybs=yai1+ya1·by

[0114] *Int(by/yas1) is a maximum integer which does not exceed(by/yas1)

[0115] The area divider 211 counts the main and sub scanningsynchronizing signals. When the pixel corresponding to the α4 appears inthe image data in the work memory 209 as shown in FIG. 12, the dividerconverts the area coordinate indicated by a rectangular block (α1, α2,α3, α4) to the coordinate in the work memory 209, and outputs thecoordinate to the averaging unit 212. Additionally, the pixels shown inFIG. 13 are reversed in order both in the main and sub scanningdirections in the work memory 209 of FIG. 12.

[0116] The averaging unit 212 uses the rectangular block area coordinatein the work memory 209 to calculate the sum of the pixel values in thearea, and a value obtained by dividing the sum by the number of pixelsin the area is stored in the area of the work memory 209.

[0117] Moreover, when the block averaging processing includes theoutside of the area (periphery of a real image shown by slashes of FIG.13), the processing is performed in accordance with states of fourpoints as follows:

[0118] if ((α1 is outside the area and α2 is outside the area) or (α3 isoutside the area and α4 is outside the area) upper or lower end of thereal image){

[0119] /*processing 1: through*/

[0120] the input pixel is outputted as it is;

[0121] }else if (α1 is outside the area and α3 is outside the area: theleft end of the real image){

[0122] /*processing 2: substituting the pixel value of the left end, andaveraging*/

[0123] an arbitrary area pixel P6(i′, j)=P6(o, j) is subjected to theaveraging processing;

[0124] /*i′ denotes a main scanning coordinate of the pixel outside thearea, j denotes a sub scanning coordinate of the pixel outside thearea*/

[0125] }else if (α2 is outside the area and α4 is outside the area: theright end of the real image){

[0126] /*processing 3: substituting the pixel value of the right end,and averaging*/

[0127] an arbitrary area pixel P6(i′, j)=P6(width−1, j) is subjected tothe averaging processing;

[0128] /*i′ denotes the main scanning coordinate of the pixel outsidethe area, j denotes the sub scanning coordinate of the pixel outside thearea*/

[0129] /*width denotes a size of the image data in the main scanningdirection*/

[0130] }

[0131]FIG. 6 is a schematic diagram in which the screen pattern isassociated with the rectangular block for the averaging processing, andxd1=4, yd1=4, xa1=4, ya1=2, yas1=2. FIG. 14 shows a constitution exampleof a block averaging processing parameter.

[0132]FIG. 15 is a block diagram showing a constitution of the imageprocessor according to a fifth embodiment of the present invention. Theconstitution of the image processor is different from that of FIG. 11 inthat the γ correction processor 96 e and block averaging section 96 dare arranged in this order in the previous stage of the patternselecting processor. The operation of the block averaging section 96 dis similar to that of the aforementioned embodiment.

[0133]FIG. 16 shows a constitution of a pattern selecting processor 96 faccording to a sixth embodiment of the present invention. For thepattern selecting processor 96 f, a correspondence pattern conversiontable chng1 (65536) 208 is disposed between the pattern table 203 andthe pattern selecting signal combiner 202 of FIG. 3. The system CPU 91refers to the pattern table ditw1 (65536) and table chng1 (65536), andoutputs the image signal Pout based on the signal Adr constituted bycombining the input image signal Pin and position signal Loc as follows.

[0134] Pout=ditw1[chng1[Adr]]

[0135] This can realize effective use of bit precision of the patterntable for storing the screen pattern which has non-linear half toneproperty. Concretely, association between the image signal and thepattern table can be changed by changing the content of thecorrespondence pattern change table 208.

[0136]FIG. 17 shows a constitution of a pattern selecting processor 96 gaccording to a seventh embodiment of the present invention. The patternsize fixed in the pattern selecting processor 96 a of FIG. 3 is changedfor each screen pattern. That is, a pattern table 216 stores the screenpattern which has various sizes. The screen pattern having anappropriate size is selected in accordance with the value of the imagesignal Pin. For example, when the image signal Pin is small (density islow), a large screen pattern is selected.

[0137] A pattern size information table 214 is added to the patternselecting processor 96 g. During calculation of the address (Loc) in thepattern table, a pattern selecting signal combiner 215 reads sizeinformation from the pattern size information table 214, the patternwith the appropriate size is selected, and an in-image position signal(x, y) is used to calculate the address Adr of the pattern table 216.

[0138]FIG. 18 shows a constitution of a pattern selecting processor 96 haccording to an eighth embodiment of the present invention. The patternselecting processor 96 h subjects a color image signal Pin to the screenprocessing. When the image signals of a plurality of channels (colorimage signals) are processed, a reading position of the pattern table203 is changed, and output screen pattern therefore differs with color.Thereby, a probability that different-color dots are outputted in thesame position can be lowered, and color unevenness of the output imagecan be suppressed. An in-pattern position calculator 218 changes amethod of calculating the in-pattern position for each channel asfollows.

[0139] The position Loc of a first channel (e.g., cyan) is calculated asfollows.

[0140] yy=y%yd1

[0141] yya=(y/yd1)%xd1

[0142] xx=(x+yya*xds1)%xd1

[0143] Loc=yy*xd1+xx

[0144] The position Loc of a second channel (e.g., magenta) iscalculated as follows.

[0145] yy=y%yd1

[0146] yya=(y/yd1)%xd1

[0147] xx=xd1−(x+yya*xds1)%xd1

[0148] Loc=yy*xd1+xx

[0149] Therefore, in the present embodiment, an effect similar to theeffect obtained by changing the pattern for each color is obtained.

[0150]FIG. 19 shows a constitution of a pattern selecting processor 96 iaccording to a ninth embodiment of the present invention. The patternselecting processor 96 i performs different screen processings inparallel to one another, and changes the output in response to a patterntable change signal. A character/photograph identification signal servesas the pattern table change signal for the image processing in acharacter area/photograph area in PPC.

[0151] An in-pattern position calculator 201 a, pattern selecting signalcombiner 202 a, and pattern table 203 a constitute, for example, asignal processing block for the character area. An in-pattern positioncalculator 201 b, pattern selecting signal combiner 202 b, and patterntable 203 b constitute, for example, a signal processing block for thephotograph area. A size of the pattern table 203 a for the characterarea is smaller than that of the pattern table 203 b for the photographarea. A selector 219 selects and outputs a reference output of one ofthe pattern tables 203 a and 203 b in response to the pattern tablechange signal.

1. An image processing apparatus comprising: a pattern table whichstores a plurality of screen patterns which include a predeterminednumber of pattern data and have different data patterns; an in-patternposition calculator which generates an in-pattern position signalindicating a position of an input image signal in said screen patternfrom a main scanning synchronizing signal and a sub scanningsynchronizing signal; a pattern selecting signal combining section whichgenerates a pattern selecting signal for selecting a specified patternin said pattern table from said input image signal, combines the patternselecting signal with said in-pattern position signal supplied from saidin-pattern position calculator, and supplies an address in the patterntable; and a pattern table reading section which reads pattern datacorresponding to the address in said pattern table from said patterntable and supplying image data.
 2. The apparatus according to claim 1,wherein said pattern data read from said pattern table by said patterntable reading section is a pulse width signal, said apparatus furthercomprises: a reference position table which stores reference positiondata for defining a position in a pixel in which the image correspondingto the pulse width signal read from said pattern table is to be formed;a reference position table reading section which reads said referenceposition data in said reference position table based on said in-patternposition signal supplied from said in-pattern position calculator, andoutputs a pulse position signal; and a signal combining section whichcombines said pulse width signal read by said pattern table readingsection and said pulse position signal read from the reference positiontable, and generates an image signal having a width corresponding tosaid pulse width signal in said reference position in each pixel.
 3. Animage processing apparatus comprising: a pattern table which stores aplurality of screen patterns including a predetermined number of patterndata and having different data patterns; an in-pattern positioncalculator which generates an in-pattern position signal indicating aposition of an input image signal in said screen pattern from a mainscanning synchronizing signal and a sub scanning synchronizing signal; apattern selecting signal combining section which generates a patternselecting signal for selecting a specified pattern in said pattern tablefrom said input image signal, and calculates an address in the patterntable and data for interpolation for use in an interpolation processingfrom the pattern selecting signal and said in-pattern position signalsupplied from said in-pattern position calculator; an interpolationoriginal data reading section which reads two consecutive pattern datain an address space of said pattern table as interpolation original datafrom said pattern table based on the address in said pattern tablecalculated by said pattern selecting signal combining section; and aninterpolation processor which uses said data for interpolationcalculated by said pattern selecting signal combining section, subjectssaid two interpolation original data read by said interpolation originaldata reading section to the interpolation processing, and supplies aresult of the interpolation processing as image data.
 4. The apparatusaccording to claim 3, wherein said interpolation processor provides saidinterpolation processing result as a pulse width signal, said apparatusfurther comprising: a reference position table which stores referenceposition data for defining a position in a pixel in which the imagecorresponding to the pulse width signal read from said interpolationprocessor is to be formed; a reference position table reading sectionwhich reads said reference position data in said reference positiontable based on said in-pattern position signal supplied from saidin-pattern position calculator, and outputs a pulse position signal; anda signal combining section which combines said pulse width signal readby said interpolation processor and said pulse position signal read fromthe reference position table, and generates an image signal having awidth corresponding to said pulse width signal in said referenceposition in each pixel.
 5. The apparatus according to claim 2, furthercomprising: a block averaging processor which divides the inputted imageinto blocks based on the main scanning synchronizing signal and the subscanning synchronizing signal, performs an averaging processing of theimage data with respect to each block, and outputs the image datasubjected to the averaging processing; and a α correcting selectionwhich subjects an image signal outputted from the block averagingsection to α correction and outputting an α-corrected image signal,wherein said α-corrected image signal outputted from said y correctingselection is supplied to said pattern selecting signal combiningsection.
 6. The apparatus according to claim 2, further comprising: a αcorrecting selection which subjects an inputted image signal to αcorrection and outputs an α-corrected image signal; and a blockaveraging section which divides said α-corrected image outputted fromsaid αcorrecting section into blocks based on the main scanningsynchronizing signal and the sub scanning synchronizing signal, performsan averaging processing of the image data with respect to each block,and outputs the image data subjected to the averaging processing,wherein the image data outputted from the block averaging section issupplied to said pattern selecting signal combining section.
 7. Theapparatus according to claim 1, further comprising: a correspondencepattern change table which, disposed between said pattern selectingsignal combining section and said pattern table, changes acorrespondence between said input image signal and the pattern data insaid pattern table, wherein the correspondence between said input imagesignal and said pattern data is changed by rewriting a content of aconversion table.
 8. An image processing apparatus comprising: a patterntable which stores a plurality of screen patterns which have differentsizes; a pattern size information table which stores size informationfor each said screen pattern; an in-image position calculator whichgenerates an in-image position signal indicating a position of an inputimage signal in an image from a main scanning synchronizing signal and asub scanning synchronizing signal; a pattern selecting signal combiningsection which reads the size information of the corresponding screenpattern from said pattern size information table based on the inputimage signal, and uses the size information and said in-image positionsignal to calculate an address in the pattern table; and a pattern tablereading section which reads image data in said pattern tablecorresponding to the address in said pattern table.
 9. An imageprocessing apparatus comprising: a channel dividing section whichdivides an image signal of a plurality of channels into the imagesignals of the respective channels; a pattern table which stores aplurality of screen patterns which include a predetermined number ofpattern data and have different data patterns; an in-pattern positioncalculator which generates different in-pattern position signalsindicating positions of the input image signals in said screen patternfor the respective channels from a main scanning synchronizing signaland a sub scanning synchronizing signal; a pattern selecting signalcombining section which generates a pattern selecting signal forselecting a specified pattern in said pattern table for each channelfrom the input image signal supplied from said channel dividing section,combines the pattern selecting signal with the in-pattern positionsignal supplied for each channel from said in-pattern positioncalculator, and supplies an address in said pattern table for eachchannel; and a pattern table reading section which reads pattern datacorresponding to the address in the pattern table of each channel fromsaid pattern table and supplying image data.
 10. An image processingapparatus comprising: a first pattern table which stores a plurality ofscreen patterns which include a first predetermined number of patterndata and have different data patterns; a second pattern table whichstores a plurality of screen patterns which include a secondpredetermined number of pattern data and have different data patterns; afirst in-pattern position calculator which generates an in-patternposition signal indicating a position of an input image signal in thescreen pattern in said first pattern table from a main scanningsynchronizing signal and a sub scanning synchronizing signal; a secondin-pattern position calculator which generates an in-pattern positionsignal indicating the position of the input image signal in the screenpattern in said second pattern table from the main scanningsynchronizing signal and the sub scanning synchronizing signal; a firstpattern selecting signal combining section which generates a patternselecting signal for selecting a specified pattern in said first patterntable from said input image signal, combines the pattern selectingsignal with said in-pattern position signal supplied from said firstin-pattern position calculator, and supplies an address in said firstpattern table; a second pattern selecting signal combining section whichgenerates the pattern selecting signal for selecting the specifiedpattern in said second pattern table from said input image signal,combines the pattern selecting signal with said in-pattern positionsignal supplied from said second in-pattern position calculator, andsupplies the address in said second pattern table; a first pattern tablereading section which reads pattern data corresponding to the address insaid first pattern table from said first pattern table and supplyingimage data; a second pattern table reading section which reads patterndata corresponding to the address in said second pattern table from saidsecond pattern table and supplies the image data; and a signal selectingsection which selects and outputs one of the image data supplied fromsaid first and second pattern table reading sections in response to aninputted pattern table change signal.
 11. The apparatus according toclaim 1, wherein the image data read from said pattern table in responseto the same in-pattern position signal monotonously changes with a sizeof said pattern selecting signal.
 12. The apparatus according to claim3, wherein the image data read from said pattern table in response tothe same in-pattern position signal monotonously changes with a size ofsaid pattern selecting signal.
 13. The apparatus according to claim 1,wherein the image data read from said pattern table in response to thesame in-pattern position signal changes an increase/decrease directionin at least one portion in accordance with a size of said patternselecting signal.
 14. The apparatus according to claim 3, wherein theimage data read from said pattern table in response to the samein-pattern position signal changes an increase/decrease direction in atleast one portion in accordance with a size of said pattern selectingsignal.
 15. The apparatus according to claim 1, further comprising: ascanner section which optically reads a draft, and supplies the imagesignal corresponding to a draft image to said pattern selecting signalcombining section; and a printer section which forms the image on acopying paper based on the image data supplied from said pattern tablereading section.
 16. The apparatus according to claim 2, furthercomprising: a scanner section which optically reads a draft, andsupplies the image signal corresponding to a draft image to said patternselecting signal combining section; and a printer section which formsthe image on a copying paper based on the image data supplied from saidsignal combining section.
 17. The apparatus according to claim 3,further comprising: a scanner section which optically reads a draft, andsupplies the image signal corresponding to a draft image to said patternselecting signal combining section; and a printer section which formsthe image on a copying paper based on the image data supplied from saidsignal combining section.
 18. An image processing method comprising thesteps of: storing a plurality of screen patterns which include apredetermined number of pattern data and have different data patterns asa pattern table in a storage; generating an in-pattern position signalindicating a position of an input image signal in said screen patternfrom a main scanning synchronizing signal and a sub scanningsynchronizing signal; generating a pattern selecting signal forselecting a specified pattern in said pattern table from said inputimage signal, combining the pattern selecting signal with saidin-pattern position signal, and supplying an address in the patterntable; and reading pattern data corresponding to the address in saidpattern table from said pattern table and supplying image data.
 19. Themethod according to claim 18, wherein said pattern data read from saidpattern table is a pulse width signal, said method further comprises:storing reference position data for defining a position in a pixel inwhich the image corresponding to the pulse width signal read from saidpattern table is to be formed as a reference position table in astorage; reading said reference position data in said reference positiontable based on said in-pattern position signal, and outputting a pulseposition signal; and combining said pulse width signal and said pulseposition signal, and generating an image signal having a widthcorresponding to said pulse width signal in said reference position ineach pixel.
 20. An image processing method comprising the steps of:storing a plurality of screen patterns including a predetermined numberof pattern data and having different data patterns as a pattern table ina storage; generating an in-pattern position signal indicating aposition of an input image signal in said screen pattern from a mainscanning synchronizing signal and a sub scanning synchronizing signal;generating a pattern selecting signal for selecting a specified patternin said pattern table from said input image signal, and calculating anaddress in the pattern table and data for interpolation for use in aninterpolation processing from the pattern selecting signal and saidin-pattern position signal; reading two consecutive pattern data in anaddress space of said pattern table as interpolation original data fromsaid pattern table based on the address in said pattern table; and usingsaid data for interpolation, subjecting said two interpolation originaldata to the interpolation processing, and supplying a result of theinterpolation processing as image data.
 21. The method according toclaim 20, wherein said step of performing the interpolation processingcomprises a step of providing said interpolation processing result as apulse width signal, said method further comprising: storing referenceposition data for defining a position in a pixel in which the imagecorresponding to said pulse width signal is to be formed as a referenceposition table in a storage; reading said reference position data insaid reference position table based on said in-pattern position signal,and outputting a pulse position signal; and combining said pulse widthsignal and said pulse position signal, and generating an image signalhaving a width corresponding to said pulse width signal in saidreference position in each pixel.
 22. An information storage mediumwhich includes a program comprising the steps of: storing a plurality ofscreen patterns which include a predetermined number of pattern data andhave different data patterns as a pattern table in a storage; generatingan in-pattern position signal indicating a position of an input imagesignal in said screen pattern from a main scanning synchronizing signaland a sub scanning synchronizing signal; generating a pattern selectingsignal for selecting a specified pattern in said pattern table from saidinput image signal, combining the pattern selecting signal with saidin-pattern position signal, and supplying an address in the patterntable; and reading pattern data corresponding to the address in saidpattern table from said pattern table and supplying image data.
 23. Theinformation storage medium according to claim 22, wherein said patterndata read from said pattern table is a pulse width signal, the programfurther comprises: storing reference position data for defining aposition in a pixel in which the image corresponding to the pulse widthsignal supplied from said pattern table is to be formed as a referenceposition table in a storage; reading said reference position data insaid reference position table based on said in-pattern position signal,and outputting a pulse position signal; and combining said pulse widthsignal and said pulse position signal, and generating an image signalhaving a width corresponding to said pulse width signal in saidreference position in each pixel.
 24. An information storage mediumwhich includes a program comprising the steps of: storing a plurality ofscreen patterns including a predetermined number of pattern data andhaving different data patterns as a pattern table in a storage;generating an in-pattern position signal indicating a position of aninput image signal in said screen pattern from a main scanningsynchronizing signal and a sub scanning synchronizing signal; generatinga pattern selecting signal for selecting a specified pattern in saidpattern table from said input image signal, and calculating an addressin the pattern table and data for interpolation for use in aninterpolation processing from the pattern selecting signal and saidin-pattern position signal; reading two consecutive pattern data in anaddress space of said pattern table as interpolation original data fromsaid pattern table based on the address in said pattern table; and usingsaid data for interpolation, subjecting said two interpolation originaldata to the interpolation processing, and supplying a result of theinterpolation processing as image data.
 25. The information storagemedium according to claim 24, wherein said step of performing theinterpolation processing comprises a step of providing saidinterpolation processing result as a pulse width signal, the programfurther comprises: storing reference position data for defining aposition in a pixel in which the image corresponding to said pulse widthsignal is to be formed as a reference position table in a storage;reading said reference position data in said reference position tablebased on said in-pattern position signal, and outputting a pulseposition signal; and combining said pulse width signal and said pulseposition signal, and generating an image signal having a widthcorresponding to said pulse width signal in said reference position ineach pixel.